Go to Settings > About and tap More Information. Phone will show you the MAC address and other details:

  • Name
  • Model
  • Carrier
  • Software
  • OS Version
  • Firmware revision number
  • Hardware revision number
  • Radio Software version
  • Chip SOC version
  • Radio Hardware version (Windows Phone 7)
  • Bootloader version (Windows Phone 7)
  • MAC Address 
  • IMEI
  • SIM ID
  • IMS